1. Field of the Invention
A present invention relates to a transient voltage detecting circuit for an electronic system having a plurality of power supplies. The circuit, according to the present invention, can detect a positive or negative transient voltage once that occurs at each power supply.
2. Description of the Prior Art
Typical electronic systems, particularly integrated circuits, have self-protecting precautions against surge, glitch, overvoltage, and other undesirable transient voltages, so as to protect the systems from wrong operations, crash, or damage of components owing to the above-mentioned transient voltages.
The self-protecting precautions adopted by the electronic systems in accordance with transient voltages focus on detecting transient voltages rapidly and accurately. Please refer to the U.S. Pat. No. 5,999,392 for the prior art of detecting transient voltage. U.S. Pat. No. 5,999,392 disclosed an auto resetting circuit with a function of detecting transient voltages; it is used for detecting unusual changes in voltages between the power supplies and the grounds in electronic systems in order to reset in time.
Nowadays, electronic systems are more complex in design, and they also comprise a plurality of power supplies for supporting different voltages for each component of the electronic systems. However, prior arts of detecting transient voltage aimed at only one power supply, or one ground, or transient voltages occurring between one power supply and one ground. A circuit for detecting transient voltages at a plurality of power supplies is still lacked up to now.
Therefore, a major objective of the present invention is to provide a transient voltage detecting circuit for detecting a plurality of power supplies of an electronic system according to the present invention.
Besides, the prior arts about transient voltage detection mostly employ components relating to or referring to the power supply of the electronic system, such as NAND gate, NOR gate, NOT gate, etc. As soon as a transient voltage occurs, the components relating to or referring to the power supply of the electronic system may not be able to remain their original electric characteristics. Therefore, the accuracy of a transient voltage detected by the transient voltage detecting circuit with the components relating to or referring to the power supply of the electronic system is not reliable.
Consequently, another objective of the present invention is to provide a transient voltage detecting circuit for detecting changes of power supplies, without having to maintain a stable main power according to the components of the transient voltage detecting circuit.